Heat Flow and the Seismogenic Zone in Southern California

Colin F. Williams

USGS, Menlo Park, CA

U.S. Department of the InteriorU.S. Geological Survey

Depth ofseismicity inSouthernCalifornia(after Nazarethand Hauksson,2004)

Heat Flow in California

Landers EQ, Heat Flow and Seismic-Aseismic Transition

Heat Flow in Ventura and LA Basins

SHLK

RDS

Observations

Observed pattern of seismicity depth cut-off Observed pattern of seismicity depth cut-off consistent with variations in heat flowconsistent with variations in heat flow Imperial Valley – Hi HF and Shallow SeismicityImperial Valley – Hi HF and Shallow Seismicity Landers – Consistent Variations in HF, Seismicity and Landers – Consistent Variations in HF, Seismicity and

Rupture depth along strikeRupture depth along strike Ventura Basin – Lo HF and Deep SeismicityVentura Basin – Lo HF and Deep Seismicity San Gregorio Pass – No HF ConstraintSan Gregorio Pass – No HF Constraint

Temperature for the seismic-aseismic transition is Temperature for the seismic-aseismic transition is ~350 to 400 ~350 to 400 ooC for most of southern California but is C for most of southern California but is lower (~250-300 lower (~250-300 ooC ??) in the Mojave, probably due C ??) in the Mojave, probably due to lithologic variationsto lithologic variations

Improved EQ catalogues key to quantitative Improved EQ catalogues key to quantitative evaluationevaluation